1. Field of the invention
The present invention relates to a method and apparatus for removing moisture from ambient air as it moves into, or out of, a vehicle lamp housing. More particularly, the present invention relates to such a method and apparatus in which a filtering fiber mat, containing a regenerable desiccant material, is contained within a filter housing, which can be placed in fluid communication with a vent passage of a vehicle lamp housing.
2. Description of the Background Art
In the automotive industry, high humidity within isolated vented vehicle lamp housings, leading to water condensation on the inner surfaces of the lamp housings, poses a recurring problem in certain vehicles. While not a widespread problem, this problem is recurrent enough to cause some concern. It is believed that this situation is caused by the following conditions.
First, during operation of a vehicle lamp such as, for example, a headlamp, of a type which is disposed within a lamp housing that is vented to air outside the unit, the heat of the bulb causes expansion of the air inside of the lamp housing, forcing the heated air outwardly from the housing through one or more vent tubes or openings therein. This expulsion of air from the housing results in less air mass being present in the housing, after a period of operation, than was present when the lamp was cold.
Later, when the vehicle is parked and the lamp is turned off, the ambient temperature inside of the lamp housing gradually cools, and the air left in the housing contracts, thereby lowering the pressure inside the housing and drawing fresh external air into the housing through the vent(s).
When conditions outside the lamp housing include a high level of humidity, the replacement air drawn into the housing is humid air, which may contain tiny suspended water droplets and/or evaporated water in the gas phase. As the lamp housing continues to cool, moisture, from humid air which has been newly drawn into the lamp housing, may precipitate and condense out of the air to form liquid water, and such water may be deposited on the internal surfaces of the housing.
Once a high level of moisture becomes established inside of a lamp housing, it may persist and be difficult to get rid of, because the vent hole or holes are relatively small, and turning the lamp back on may cause re-evaporation of liquid condensate within the housing. A cycle of condensation and evaporation inside the lamp housing may follow, without significantly reducing the humidity level therein. Repetitive cycles of evaporation and condensation, under the above-described conditions, may actually exacerbate the problem and promote deterioration of electrical components of the lamp.
Moisture buildup in headlamp assemblies results in customer dissatisfaction and an expensive replacement of the entire lamp assembly. Such condensation can occur immediately following production or can show up much later in the useful life of the vehicle.
There is a trend in the automotive industry to mount the vehicle headlamp in an enclosed plastic headlamp assembly. A halogen or tungsten lamp is mounted within a plastic assembly, which contains the reflector, lens, positioning mechanism, and lamp fixture. In addition, there has been a trend toward the use of clear plastic lenses, without texture or embossing, in such headlamp assemblies. Moisture buildup becomes much more obvious with this type of lens.
Some efforts have been made in the art to overcome the aforementioned problem. Many different types of designs are known for lamp housings having particular designs for ventilator ports or tubes formed therein, such as those disclosed in U.S. Pat. No. 5,457,616 and 5,702,178.
U.S. Pat. No. 5,406,467 discloses a ventilation system for a vehicle lamp in which a baffle is placed inside of a rubber hose serving as a ventilation tube, and a porous filter plug is placed inside the tube at the top of the baffle, to try and minimize the amount of liquid water which may enter into the lamp housing.
Some designs are also known for placing desiccant materials inside of lamp housings, which may be done in conjunction with ventilation tubes. Examples of these types of desiccant apparatus are given by U.S. Pat. Nos. 4,612,607, 4,731,709, 4,739,458, 4,755,917, and 4,809,144.
U.S. Pat. No. 4,755,917 generically suggests using a granular, reversibly-acting hygroscopic desiccating agent in a ventilation flow housing of a vehicle lamp. However, this reference fails to specifically mention any particular desiccating agent or agents which are usable in connection therewith. This same reference also suggests that a duct, filled with a desiccating agent, may be located in a hood disposed in the path of a light beam from an incandescent bulb of a headlight. The reference does not depict, illustrate or give any specific information as to how to arrange the duct containing the desiccant material with respect to such a hood.
Several patents exist relating to bulb shields to cover the intense light exiting directly from a vehicle lamp. Some examples of such bulb shield designs are disclosed in U.S. Pat. Nos. 3,553,519, 4,722,039, 5,253,153, 5,660,462, and 5,850,124.
The assignee of the present invention has invented a type of wicking fiber material, which is useful in a variety of applications. These fibers are disclosed in U.S. Pat. No. 5,057,368 to Largman et al.
A need still exists in the art for an improved dehydrating method and filter apparatus for placement in fluid communication with the vent opening of a lamp housing, to filter air as it enters and leaves the housing, and to minimize the amount of water allowed into and retained within the housing. Preferably, the desiccant used in such a filter apparatus would be capable of being regenerated, so that it could use the natural heating and cooling cycle of the lamp to regenerate the desiccant material, and would therefore be usable throughout an extended life through repeated heating and cooling cycles of the lamp.
The present invention provides a regenerable desiccant filter assembly for use in a vehicle lamp housing. The present invention also provides a method of dehydrating air flowing through a ventilation opening in a vehicle lamp housing, using the inventive apparatus.
A filter assembly in accordance with the present invention, generally, includes: a) a hollow body defining a chamber therein, the hollow body having an inlet and an outlet formed therein to allow air to flow from an area outside of the hollow body into and through the hollow body; b) a substrate housed within the hollow body; and c) a desiccant composition distributed on the substrate.
The hollow body may be a tubular member, which may have a single inlet and a single outlet covered by water-resistant screen members, or may be a foraminous member. In one embodiment, the hollow body may be combined with a bulb shield for a vehiclular bulb. In another embodiment, the hollow body may be an integral part of a bulb socket housing.
Preferably, the substrate is a non-woven fiber material which has hollow internal cavities formed therein, and extended openings formed in the sides thereof, in which the internal cavities communicate with the outside environment through the extended openings.
In a fixed bed format, the present invention provides a liquid desiccant with superior water removal properties as compared to solid granular desiccants.
Also preferably, the desiccant composition is an alkali halide or an alkaline earth halide. Most preferably the desiccant composition is selected from the group consisting of lithium chloride, calcium chloride and magnesium chloride.
Accordingly, it is an object of the present invention to provide a method and apparatus for reducing the humidity of air passing through a ventilation opening of a vehicle lamp housing.
It is a further object of the present invention to provide an improved method and apparatus for reducing the humidity of air within a lamp housing.
It is yet a further object of the present invention to provide an improved method and apparatus for reducing air humidity, which involves the use of a regenerable desiccant material.
It is a still further object of the present invention to provide a method and apparatus of the type described which will be operable after a temperature reduction of only a few degrees from an operating temperature within a lamp housing.
For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts.